Combination bullet-perforating gun and shaped charge perforator apparatus and method

ABSTRACT

A bullet-perforating gun and a shaped charged perforator are aligned in a common plane within a tool suitable for passage through an earth borehole. One or both of the perforators have their axes, respectively, inclined such that the resulting two perforations intersect before either reaches its normal depth of penetration. The perforators are arranged to fire simultaneously. Because of the time difference in speed of action, the shaped charge perforates first. At a time later, the bullet makes a perforation which breaks into the shaped charge perforation. In escaping through the shaped charge hole, the gases flush out the pulverized material from the bullet perforation, the shaped charge perforation and any enlargement of the common portions of the two holes.

United States Patent [72] Inventor Floyd 0. Bohn Houston. Tea.

[21] Appl. No. 866,834

[22] Filed Oct. 16, 1969 (45] Patented Nov. 16, 1971 [73] AssigneeDresser lndustrles, Inc.

Dallas, Tex.

[ 54] COMBINATION BULLET-PERFORATING GUN AND SHAPED CHARGE PERFORATORAPPARATUS AND METHOD 5 Claims, 6 Drawing Figs.

[51] lnt.Cl E2111 43/117 [50] Field of Search l75/4.57-4.6;

[56] References Clted UNITED STATES PATENTS 2,928,658 3/1960 Miner17514.6 x 3,080,005 3/1963 Porter l75/4.6 x

3,089,416 5/1963 Gilbert 175/411 3,101,051 8/1963 Gilbert..... 175/41:3,348,621 10/1967 Schuster 175/41; X

ABSTRACT: A bullet-perforating gun and a shaped charged perforator arealigned in a common plane within a tool suitable for passage through anearth borehole. One or both of the perforators have their axes,respectively, inclined such that the resulting two perforationsintersect before either reaches its normal depth of penetration. Theperforutors are arranged to fire simultaneously. Because of the timedifference in speed of action, the shaped charge perforates first. At atime later, the bullet makes a perforation which breaks into the shapedcharge perforation. ln escaping through the shaped charge hole, thegases flush out the pulverized material from the bullet perforation, theshaped charge perforation and any enlargement of the common portions ofthe two holes.

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FIG-4B FIG.4C

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FIG. 3

A T TOR/V5 Y COMBINATION BULLET-PERFORA'I'ING GUN AND SHAPED CHARGEPERFORATOR APPARATUS AND METHOD BACKGROUND OF THE. INVENTION Thisinvention relates generally to improved method and apparatus useful inperforation of oil and gas wells and the like. More particularly, butnot by way of limitation, the invention relates to improved methods andapparatus for completion of a well in earth formations.

Generally, in the completion of oil and gas wells and the like, anelongated metal casing is positioned in the well bore. Due to theirregularity of the well bore and due to the difference in diameterbetween the well bore and the metal casing, a cementitious material isusually pumped into the annular space, The cement serves to pennanentlyfix the metal casing in the well bore and to prevent migration of wellfluids through the annular space. It is obvious that the metal casingand the cement disposed adjacent a productive formation will prevent theflow of fluids from the formations into the interior of the casing.Therefore, the practice has been to perforate the metal casing, thecement and the adjacent formation by the use of either shaped charge orbullet perforators. The perforators are lowered into the casing to aposition adjacent the formation of interest and then fired from theearth's surface through an appropriate electrical circuit.

No matter which type of perforator has been used by those in the art,both the bullet and the shaped charged perforators break down theformation while making a hole. The pulverized matrix and formationelements are compacted in some portions of the hole. This debris isdetrimental to both the productivity and fluid injectivity ofaperforation.

It is therefore the primary object of the present invention to provideimproved methods and apparatus for perforating earth formationssurrounding an earth borehole; and it is another object of the inventionto provide methods and apparatus useful in perforating earth formationssurrounding an earth borehole wherein portions of the debris incident tothe perforation are removed coincidentally with the formation of debriswithin the hole.

The objects of the invention are achieved, generally, by method andapparatus within the preferred embodiment wherein a shaped chargeperforation intersects with a bullet perforation and the gases formedtherefrom are used to clear out the debris from the holes. These andother objects, fealures, and advantages of the present invention willbecome more apparent from a reading of the following detaileddescription and accompanying drawing, in which:

FIG. I is a cross-sectional view of a shaped charge constructed inaccordance with the invention;

FIG. 2 is a cross-sectional view of a bullet gun perforator constructedin accordance with the invention;

FIG. 3 is a vertical cross section illustrating the combined perforatingapparatus constructed in accordance with the invention disposed in acased well bore; and

FIGS. 4A. B and C are a series of vector diagrams illustratingalternative angular relationships between the perforators according tothe invention. Referring now to the drawing in detail, and especially toFIG. I, there is illustrated therein a shaped charge constructed inaccordance with the invention. The shaped charge 10 includes a hollowbody l2, an explosive material I4 partly filling the interior of thehollow body I2. and a cap I6 closing one end of the hollow body 12.

The explosive material I4 has a conical cavity 18 in the end thereofadjacent the cap l6. A liner 20, which is also of conical configuration.is located in the hollow body I2 in jLlX' taposition with the surface ofthe explosive material 14 forming the cavity 18. The liner 20 may beconstructed from relatively thin sheet metal. but is preferablyconstructed from a granular metal as disclosed in US. Pat. No. 3,255,659issued on June 14, I966 to Alexis A. Venghiattis.

A plurality of particles 2l are located between the surface of theexplosive material l4 and the liner 20. The particles 2l are preferablyformed from an inert material and preferably have at least one dimensionthat is not less than one-half the diameter of the perforation that isformed upon detonation of the shaped charge 10.

As will be understood by those skilled in the art of shaped charges, theconical cavity ID in the charge 10 produces the so-called Monroe effectupon detonation that results in a high energy, high-speed jet ofsufficient energy magnitude to form perforations. The rate of detonationof such a shaped charge and the subsequent jet stream is in the order of25,000 lt/sec.

Referring now to FIG. 2, there is illustrated a bullet perforation guna'esembly 30 comprised of a generally cylindrical tubular gun body 31.The gun body 3] may be formed of a generally elongated solid steelcylinder of sumcient strength and solidity to withstand the pressuresgenerated by the firing of the gun. The gun body 31 is provided with thelaterally extending coaxial bores 26 and 28. The smaller diameter bore26 extends innermost and forms the charge chamber. Positioned in thecharge chamber 26 is a combined propellant charge and bullet unit 34. Abore 36 having an initial tapered position 38 extends from the rear wallof the charge chamber 26 to a cylindrical cavity 40 in the peripheralwall of the gun body 31. The tapered portion 38 of the bore 36accommodates the tapered head 42 of a firing pin 44 which extendsthrough the bore 36 into the cavity 40 where the electrical connectionto the firing pin 44 is made to conductor 46. The tapered head 42 andthe firing pin 44 are insulated from the gun body. A seal 48 is engagedwith the wall of the cavity to form a seal for the cavity 40 and toprevent the entrance of well fluid into the gun.

The cylindrical wall of the outer bore 28 is formed into female threadsto engage with the male threads of a generally tubular barrel member 50which has a central core 51 forming a barrel for the gun and the bullet80. Additional details for building such a gun, along with the powercharge considerations, can be found in US. Pat. No. 3,376,375 issuedApr. 2, I968 to Forrest V. Porter.

A bullet from such a gun travels in the order of 3.000 ItJsec. However,this velocity is not attained until a measurable length of time is usedin combustion of the propellant powder. initial pressure buildup andfinally acceleration of the bullet and flight through the barrel of thegun.

Thus, it should be appreciated that when a bullet gun and a shapedcharge gun are fired simultaneously, the perforating by the shapedcharge is completed before that of the bullet perforator due to thedifferences in velocity of the two perforators.

Although the preferred embodiment of the invention is directed tospecific forms of the shaped charge and bullet gun perforators, itshould especially be appreciated that such forms are merely illustrativeof types of perforators and are not meant to be a limitation upon theinvention. Other examples of shaped charge perforators are found in U.S.Pat. No. 3,358,780 issued Dec. 19, I967 to Alexis A. Venghiattis and US.Pat. No. 3,415,321 issued Dec. l0, I968 to Alex A. Venghiattis.Likewise, additional examples of bullet gun perforators are found in US.Pat. No. 2,953,971 issued Sept. 27, 1960.

Referring now to FIG. 3 of the drawing. there is illustrated a boreholeinstrument 6!) adapted to traverse a cased borehole 6l having a casing62. Between the metal casing 62 and the earth formation 64 is the cement63 as is well known in the art. The cable 65 is used to raise and lowerthe instrument 60 in the borehole and also contains the necessaryconductors for causing the perforators to be activated. The instrument60 is centered within the cased borehole by the conventional centralizermeans 77. If desired, the instrument side having the perforatorsadjacent thereto can be urged into contact with the casing as is knownin the art.

Located within the instrument 60 is a bullet perforator 30 and a shapedcharge perforator I0. The shaped charge perforator I0 is connected to aPrimacord 70, a booster 7i and a detonator 72. The detonator 72 isconnected to an electrical wire 73 through the adapter 74 to one of theconductors in the cable which leads to an electrical source (not shown)at the earth s surface (not shown). As is well known, electric currentpassing through the conductor 73 ignites the detonator 72, the booster7! and the Primacord 70. Due to the high-explosive nature of Primacord,an electrical signal appearing at the conductor 73 detonates the shapedcharge essentially simultaneously.

The bullet gun perforator 30, as explained previously with respect toFIG. 2, has connected thereto an electrical conductor 46 which passesthrough the cable 65 to the earths surface.

Although the preferred embodiment contemplates the electrical signalsfor the two types of perforators coming down separate conductors in thecable 65, the signal can be transmitted down a common conductor, onevoltage signal being used to detonate both perforators.

By having the shaped charge in a common plane with the bullet gun 30,while at the same time having their axes inclined, respectively, withrespect to the longitudinal axis '75 of the instrument 60 such that theaxes of the two perforators intersect. the perforations also intersectat a point in the earth formation 64. As explained previously, the gasflow (indicated by the arrows 76) passes through the shaped chargeperforation back into the borehole, carrying debris within the gas.

FIGS. 4A, B and C illustrate the angular relationship between theperforators for achieving the desired results. FlG. 4A illustrates thelongitudinal axis 85 of the bullet gun 30 as being substantiallyperpendicular to the longitudinal axis 75 of the instrument 60, whereasthe longitudinal axis 86 of the shaped charge 10 is inclined at an anglel with respect to axis FIG. 48 illustrates an alternative embodimentwherein axis 86 is inclined at an angle l whereas axis 85 is inclined atan angle 0, which can be the same as angle 41' ifdesired.

FIG. 4C illustrates an alternative embodiment wherein axis 85 isinclined at an angle lb while maintaining axis 86 substantiallyperpendicular to axis 75.

Thus it should be appreciated that by having one or both of the axes 85and 86 inclined with respect to axis 75, the axes 85 and 86 are alignedto intersect since they are positioned in a common plane. The anglebetween the axes 85 and 86 is preferably chosen such that theintersection within the formation occurs before either perforation wouldreach its normal depth of penetration.

Although only one bullet gun and one shaped charge are illustrated anddescribed with respect to the instrument 60, additional pairs of shapedcharges and bullet guns can be provided within the instrument 60 in asimilar manner as described for the single pair.

In addition to utilizing the difference in speed of perforation, asecond difference is used to advantage. Although there are gasesinvolved in the detonation of the high explosives used in shapedcharges, it is primarily the wave of detonation or jet that makes a holein the target. Even in soft rock targets, there is little or no evidenceof hole erosion by high-velocity gases. In contrast, the bullet obtainsits energy from the pressure of the gases resulting from the combustionof the propellant powder. Particularly in very short barrel guns, suchas the casing perforator, there is a large volume of high-pressure gasavailable for use after the bullet has left the gun barrel. Thisresidual gas leaves evidence of its ability to do work in some rocktargets. Softer rocks are eroded and the hole is quite often cleansed ofpulverized debris.

Thus, there has been described herein the preferred embodiments of a newand improved perforation method and apparatus. However, the details arepresented by way of example only and it is contemplated that manychanges and modifications can be made thereto without departing from thespirit of the invention. For example, instead of using a shaped chargein combination with a bullet gun. it is contemplated that one can useany two perforators, regardless of type, wherein one perforatorpenetrates faster than the other. Thus, a highvelocity shaped charge canbe used in combination with a lowvelocity shaped charge. Likewise, ahigh-velocity bullet gun can be used with a low-velocity bullet.

As an alternative embodiment. it should be appreciated that instead ofusing the illustrated apparatus for ignition of the pair of perforators,satisfactory results have also been obtained from using a flame trainhole to create a substantially simultaneous ignition. By having theflame train hole start in the shaped charge section and extend into thecombustion chamber of the bullet perforator, ignition of the primacordand shaped charge creates a flame, through the flame train hole, whichignites the bullet gun. Although this approach can be used with separatesections, it is quite readily adaptable to having the two perforators ina common steel bar.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

I. Perforating apparatus for use in perforating earth formationssurrounding an earth borehole, comprising:

instrument means adapted to traverse on earth borehole;

a first perforator in said instrument means having a first perforatingvelocity and aligned in a given plane;

a second perforator in said instrument means having a second perforatingvelocity different from said first perforating velocity and beingaligned in said given plane,

said first perforator and said second perforator being aligned toprovide intersecting paths of perforation before either of saidperforators reaches its normal depth of penetration within said earthformations; and

means to substantially simultaneously fire said perforators.

2. The apparatus according to claim I wherein said first perforator is ashaped charge and said second perforator is a bullet gun.

3. The apparatus according to claim I wherein the longitudinal axis ofone of said perforators is perpendicular to the longitudinal axis ofsaid instrument and the longitudinal axis of the other of saidperforators is inclined to the longitudinal axis of said instrument.

4. The apparatus according to claim I wherein the longitudinal axis ofeach of said perforators is inclined to the longitu dinal axis of saidinstrument.

5. A method of perforating the formation surrounding an earth borehole,comprising:

positioning a first perforator in said borehole wherein said firstperforator has a given rate of penetration;

positioning a second perforator in said borehole wherein said secondperforator has a rate of penetration difi'erent from said given rate,said first perforator and said second perforator being aligned in acommon plane and having their longitudinal axes arranged, respectively,to provide intersecting paths of perforation before either of saidperforators reaches its normal depth of penetration within the earthformation; and

simultaneously firing said perforators.

I 1 l 0 i

1. Perforating apparatus for use in perforating earth formationssurrounding an earth borehole, comprising: instrument means adapted totraverse on earth borehole; a first perforator in said instrument meanshaving a first perforating velocity and aligned in a given plane; asecond perforator in said instrument means having a second perforatingvelocity different from said first perforating velocity and beingaligned in said given plane, said first perforator and said secondperforator being aligned to provide intersecting paths of perforationbefore either of said perforators reaches its normal depth ofpenetration within said earth formations; and means to substantiallysimultaneously fire said perforators.
 2. The apparatus according toclaim 1 wherein said first perforator is a shaped charge and said secondperforator is a bullet gun.
 3. The apparatus according to claim 1wherein the longitudinal axis of one of said perforators isperpendicular to the longitudinal axis of said instrument and thelongitudinal axis of the other of said perforators is inclined to thelongitudinal axis of said instrument.
 4. The apparatus according toclaim 1 wherein the longitudinal axis of each of said perforators isinclined to the longitudinal axis of said instrument.
 5. A method ofperforating the formation surrounding an earth borehole, comprising:positioning a first perforator in said borehole wherein said firstperforator has a given rate of penetration; positioning a secondperforator in said borehole wherein said second perforator has a rate ofpenetration different from said given rate, said first perforator andsaid second perforator being aligned in a common plane and having theirlongitudinal axes arranged, respectively, to provide intersecting pathsof perforation before either of said perforators reaches its normaldepth of penetration within the earth formation; and simultaneouslyfiring said perforators.